A single gene fault could hold the key to a range of disorders linked to heart disease and stroke, a study has found.

A team from Yale University School of Medicine found the defect was linked to conditions such as high blood pressure and high cholesterol.

It affects the genes of the mitochondria - the energy-producing 'power plants' of the cell that are passed from mother to offspring.

The research is published online by the magazine Science.

This doesn't answer the big questions, but it does give us a new place to start looking

Professor Hugh Watkins, Oxford University

Experts hope the finding will lead to greater understanding of the causes of such disorders.

The US team's discovery stemmed from the study of one woman who had hypertension - high blood pressure - and low blood magnesium levels.

Low magnesium is relatively rare, so researchers tested her for known mutations that they had previously associated with that trait.

The woman said a number of other female relatives in her family also had low magnesium levels, which researchers said suggested there was a particular genetic condition affecting her family which had not been seen before.

They studied 142 women in the family and found there was a high frequency of high cholesterol and high blood pressure.

Around half had all three conditions.

This suggested there was a defect in the mitochondrial genome, because those genes are uniquely passed down by the mother.

New link

The researchers then carried out detailed analysis of the mitochondrial genomes of family members and found that all those who were affected had a defect within a gene linked to a specific transfer RNA (tRNA) in the mitochondria.

Transfer RNAs are involved in the construction of proteins in cells.

The family's genetic defect affected the tRNA that transports the amino acid isoleucine. Since many proteins normally contain isoleucine, this could contribute to a broad range of cell malfunctions.

Researchers found members of the family were also affected by other conditions linked to mitochondrial malfunction, such as hearing loss and migraines.

Dr Richard Lifton, who led the research, said: "There has never before been a report of a common genetic link among any of the three traits we found - low magnesium, hypertension and high cholesterol.

"This raises the general question of whether the more common forms of these traits might arise from abnormal mitochondrial function as well."

He said that, since not all family members who had the mutation had all three conditions, there must be other genetic or environmental factors which influenced whether or not someone would be affected.

He said: "It was particularly striking that the complex pattern of clustering that we see arising from this single mutation has many of the hallmarks of the kinds of clustering that we see in the general population."

However, he added: "We have identified this defect and linked it with these traits, but there remains a complex black box in between. We don't know the mechanism that links the two."

'Early stages'

Hugh Watkins, professor of Cardiovascular Medicine at Oxford University, told BBC News Online: "This doesn't answer the big questions, but it does give us a new place to start looking.

"Never before has a link been made between mitochondrial DNA defects and low magnesium levels, high cholesterol or high blood pressure."

He added: "We are still in the very early stages of this research and we are very far from treatment."

But Professor Watkins said a similar discovery of a rare genetic defect which affected how the liver handled cholesterol eventually informed work on statins, which are now widely used to reduce cholesterol levels.